As a flow rate control valve for controlling a flow rate in proportion to the output of an electromagnetic operation means, there is generally used a spool valve in which a spool arranged in the sleeve to be allowed to slide therein is brought to a position where the attractive force of an electromagnetic solenoid is balanced with the reactive force of the spring.
The spool valve is so constituted that the spool slides along the inner peripheral surface of the sleeve having ports formed in the side surface thereof. Therefore, it needs having a clearance between the sleeve and the spool, and a complete sealing cannot be attained because it is not allowed to use a seal such as rubber or the like. To enhance the sealing between the sleeve and the spool, the clearance between them must be minimized, and yet retaining sliding performance. To satisfy this requirement, however, a highly precise machining is required, resulting in an increase in cost of machining. Further, the spool valve causes malfunction if a dust or the like enters between the sleeve and the spool. In order to solve such problem of the spool valve-type flow rate control valve, the present applicant has proposed a flow rate control valve of the poppet valve type in JP-A 2000-55211.
The flow rate control valve proposed in the above JP-A 2000-55211 is of the two-way valve type of flow rate control valve which must be used in combination with another valve for changing over the intake and the exhaust, arousing such problems that the fluid circuit constitution becomes complex and that the another valve used in combination is operated with great frequency.
The present invention has been done in view of the above-mentioned facts, and its principal technical assignment is to provide a flow rate control valve of three-way valve type capable of controlling the flow rate in proportion to the output of an electromagnetic operation means by using a poppet valve means that features good sealing.